Display device and method of manufacturing the same

ABSTRACT

A display device includes a substrate, a first electrode extending in a first direction on the substrate, a first partition wall extending in the first direction on a central portion of the first electrode, a second electrode extending in parallel with the first electrode on the substrate, a second partition wall extending in the first direction on a central portion of the second electrode, and a plurality of light-emitting diodes electrically connected between the first electrode and the second electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/061,144, filed Oct. 1, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/154,856, filed on Oct. 9, 2018, which claimspriority to Korean Patent Application No. 10-2017-0133484, filed on Oct.13, 2017, and all the benefits accruing therefrom under 35 U.S.C. § 119,the content of which in its entirety is herein incorporated byreference.

BACKGROUND 1. Field

Exemplary embodiments relate to a display device and method ofmanufacturing the same, and more particularly, to a display deviceincluding an ultraminiature light-emitting diode (“LED”) and a method ofmanufacturing the same.

2. Description of the Related Art

A light-emitting diode (“LED”) has high light conversion efficiency,very low energy consumption, a semi-permanent life, and anenvironment-friendly characteristic. To use the LED for a light or adisplay device, it is desired to connect the LED between a pair ofelectrodes which may apply power to the LED. Methods of connecting theLED to the pair of electrodes may be classified into a method ofdirectly growing an LED on an electrode and a method of separatelygrowing an LED and then arranging the LED on an electrode.

SUMMARY

In a method of separately growing a light-emitting diode (“LED”) andthen arranging the LED on an electrode, when the LED is anultraminiature LED of a nano unit, it is difficult to arrange the LED onthe electrode.

One or more exemplary embodiments include a display device which mayreduce a bonding defect between an ultraminiature LED and electrodeswhich may occur when the ultraminiature LED independently manufacturedis connected between a pair of electrodes, and a method of manufacturingthe display device.

Additional exemplary embodiments will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the presented embodiments.

According to an exemplary embodiment, a display device includes asubstrate, a first electrode extending in a first direction on thesubstrate, a first partition wall extending in the first direction on acentral portion of the first electrode, a second electrode extending inparallel with the first electrode on the substrate, a second partitionwall extending in the first direction on a central portion of the secondelectrode, and a plurality of LEDs electrically connected between thefirst electrode and the second electrode.

In an exemplary embodiment, each of the plurality of LEDs may include afirst end contacting an upper surface of the first electrode and asecond end contacting an upper surface of the second electrode.

In an exemplary embodiment, the display device may further include afirst connection electrode electrically connecting the first electrodeto the first end of each of the plurality of LEDs, and a secondconnection electrode electrically connecting the second electrode to thesecond end of each of the plurality of LEDs.

In an exemplary embodiment, an interval between the first electrode andthe second electrode may be less than a length of an LED of theplurality of LEDs.

In an exemplary embodiment, an interval between the first partition walland the second partition wall may be equal to or greater than a lengthof an LED of the plurality of LEDs.

In an exemplary embodiment, a height of each of the first partition walland the second partition wall may be equal to or greater than a lengthof an LED of the plurality of LEDs.

In an exemplary embodiment, a width of a cross-section of the firstpartition wall and the second partition wall may not be reduced in adirection away from the substrate. An angle defined by an upper surfaceof the first electrode and a lateral surface of the first partition wallmay be 90° or less, and an angle defined by an upper surface of thesecond electrode and a lateral surface of the second partition wall maybe 90° or less.

In an exemplary embodiment, each of the first partition wall and thesecond partition wall may include an organic insulating material inwhich scattering particles are dispersed.

In an exemplary embodiment, the display device may further include apixel-defining layer which is arranged over the substrate and in whichan opening exposing an emission region is defined, and the plurality ofLEDs and the first and second partition walls are arranged in theemission region.

In an exemplary embodiment, the first and second partition walls mayinclude a same material as that of the pixel-defining layer.

In an exemplary embodiment, the display device may further include acapping layer filling the opening of the pixel-defining layer andcovering lateral surfaces of the first and second partition walls, arefractive index of a material of the first and second partition wallsbeing greater than a refractive index of a material of the cappinglayer.

In an exemplary embodiment, a cross-section of the first and secondpartition walls may have an inverse-tapered shape from an upper surfaceof the first and second electrodes.

According to one or more embodiments, a display device includes asubstrate, a plurality of pixels arranged in a row direction and acolumn direction over the substrate, a plurality of first power wiringsextending in the column direction over the substrate and connected topixels of the plurality of pixels arranged in a same column, and aplurality of second power wirings extending in the row direction overthe substrate and connected to pixels of the plurality of pixelsarranged in a same row, wherein each of the plurality of second powerwirings includes power electrodes respectively connected to the pixelsspaced apart from each other in the row direction and arranged in thesame row, and each of the plurality of pixels includes a thin filmtransistor (“TFT”) arranged over the substrate and connected to acorresponding power electrode among the power electrodes, a plurality offirst electrodes extending in a first direction over the substrate andelectrically connected to a corresponding first power wiring among theplurality of first power wirings, a plurality of first partition wallsextending in the first direction on the plurality of first electrodes, aplurality of second electrodes extending in the first direction over thesubstrate, electrically connected to the TFT, and alternatively arrangedwith the plurality of first electrodes, a plurality of second partitionwalls extending in the first direction on the plurality of secondelectrodes, and a plurality of LEDs electrically connected between afirst electrode of the plurality of first electrodes and a secondelectrode of the plurality of second electrodes adjacent to each other.

In an exemplary embodiment, each of the plurality of first partitionwalls may be arranged on a central line of a corresponding firstelectrode among the plurality of first electrodes, and each of theplurality of second partition walls may be arranged on a central line ofa corresponding second electrode among the plurality of secondelectrodes.

In an exemplary embodiment, a length of an LED of the plurality of LEDsmay be longer than an interval between the first electrode and thesecond electrode adjacent to each other, and may be shorter than aninterval between a first partition wall of the plurality of firstpartition walls and a second partition wall of the plurality of secondpartition walls adjacent to each other.

In an exemplary embodiment, the display device may further include apixel-defining layer which is arranged over the substrate and in whichopenings exposing an emission region of the pixels are defined, whereinthe plurality of LEDs and the plurality of first and second partitionwalls are arranged in the emission region, and a material of theplurality of first and second partition walls is same as a material ofthe pixel-defining layer.

In an exemplary embodiment, the display device may further include acapping layer filling the openings of the pixel-defining layer andcovering lateral surfaces of the plurality of first and second partitionwalls, a refractive index of a material of the plurality of first andsecond partition walls being greater than a refractive index of amaterial of the capping layer, a cross-section of the first and secondpartition walls having an inverse-tapered shape from an upper surface ofthe plurality of first and second electrodes.

According to one or more embodiments, a method of manufacturing adisplay device, the method includes forming first and second electrodesextending in a first direction on a substrate such that the first andsecond electrodes are parallel to each other, forming an organicinsulating material layer on the first and second electrodes, formingfirst and second partition walls and a pixel-defining layer defining anopening exposing an emission region by removing a portion of the organicinsulating material layer, the first and second partition wallsextending in the first direction on a central portion of the first andsecond electrodes and being arranged in the emission region, putting asolvent including a plurality of LEDs onto the first and secondelectrodes, aligning the plurality of LEDs between the first and secondelectrodes by inducing an electric field between the first and secondelectrodes, and forming a first connection electrode and a secondconnection electrode, the first connection electrode electricallyconnecting one end of each of the plurality of LEDs to the firstelectrode, the second connection electrode electrically connecting anopposite end of each of the plurality of LEDs to the second electrode.

In an exemplary embodiment, the method may further include forming acapping layer filling the opening of the pixel-defining layer andcovering lateral surfaces of the first and second partition walls, arefractive index of a material of the first and second partition wallsbeing greater than a refractive index of a material of the cappinglayer.

In an exemplary embodiment, the forming the first and second partitionwalls may include performing an exposure process on the organicinsulating material layer having photosensitivity by adjusting exposureenergy and a focal position of an exposure beam such that across-section of the first and second partition walls has aninverse-tapered shape from an upper surface of the first and secondelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other exemplary embodiments will become apparent and morereadily appreciated from the following description of the exemplaryembodiments, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a plan view of an exemplary embodiment of a display device;

FIG. 2 is a plan view of an exemplary embodiment of a portion of adisplay area DA;

FIGS. 3A to 3D are views of various embodiments of light-emitting diodes(“LEDs”);

FIG. 4A is a partial cross-sectional view of an exemplary embodiment ofthe display area taken along line A-A′ of FIG. 2 ;

FIG. 4B is a partial cross-sectional view of another exemplaryembodiment of the display area taken along line A-A′ of FIG. 2 ;

FIG. 5 is a partial cross-sectional view of a comparative example of adisplay device in which first and second partition walls are absent;

FIG. 6 is a plan view of another exemplary embodiment of a portion of adisplay area DA;

FIG. 7A is a partial cross-sectional view of another exemplaryembodiment of the display area taken along line B-B′ of FIG. 6 ;

FIG. 7B is a partial cross-sectional view of another exemplaryembodiment of the display area taken along line B-B′ of FIG. 6 ;

FIG. 8 is a plan view of another exemplary embodiment of a portion of adisplay area DA;

FIG. 9 is a partial cross-sectional view of another exemplary embodimentof the display area taken along line C-C′ of FIG. 8 ;

FIGS. 10A to 101 are cross-sectional views of an exemplary embodiment ofa process of manufacturing a display device illustrated in FIGS. 2 and4B; and

FIG. 11 is a cross-sectional view for explaining an exemplary embodimentof a process of self-aligning of an LED.

DETAILED DESCRIPTION

As the invention allows for various changes and numerous embodiments,specific embodiments will be illustrated in the drawings and describedin detail in the written description. Effects and characteristics ofinvention, and a method of accomplishing them will be apparent byreferring to content described below in detail together with thedrawings. However, the illustrated exemplary embodiments are not limitedto exemplary embodiments below and may be implemented in various forms.

Hereinafter, the invention will be described more fully with referenceto the accompanying drawings. For clear description of the invention,parts unrelated to descriptions are omitted, and like reference numeralsare used for like or corresponding elements and repeated descriptionsthereof are omitted when descriptions are made with reference to thedrawings.

It will be understood that when a layer, region, or component isreferred to as being “disposed on” another layer, region, or component,it can be directly or indirectly disposed on the other layer, region, orcomponent. That is, for example, intervening layers, regions, orcomponents may be present. Sizes of components in the drawings may beexaggerated for convenience of explanation. In other words, since sizesand thicknesses of components in the drawings are arbitrarilyillustrated for convenience of explanation, the invention is not limitedthereto.

It will be understood that when a layer, region, or component isreferred to as being “connected” to another layer, region, or component,it may be “directly connected” to the other layer, region, or componentor may be “indirectly connected” to the other layer, region, orcomponent with other layer, region, or component interposedtherebetween. For example, it will be understood that when a layer,region, or component is referred to as being “electrically connected” toanother layer, region, or component, it may be “directly electricallyconnected” to the other layer, region, or component or may be“indirectly electrically connected” to other layer, region, or componentwith other layer, region, or component interposed therebetween.

It will be understood that although the terms “first”, “second”, etc.may be used herein to describe various components, these componentsshould not be limited by these terms. These components are only used todistinguish one component from another. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will beunderstood that when a first element includes or has a second element,the first element does not exclude another element and may includeanother element unless particularly described otherwise.

In the following examples, the x-axis, the y-axis and the z-axis are notlimited to three axes of the rectangular coordinate system, and may beinterpreted in a broader sense. For example, the x-axis, the y-axis, andthe z-axis may be perpendicular to one another, or may representdifferent directions that are not perpendicular to one another.

An exemplary embodiment regarding a manufacturing method may beperformed according to a process sequence different from a processsequence described in the present specification. For example, although asecond process is described after a first process is described, thefirst process and the second process may be performed substantially atthe same time, or terms “corresponding” or “to correspond” in thespecification may mean being arranged or connected in a same row and/orcolumn. For example, it will be understood that when a first member isconnected to a “corresponding” second member among a plurality of secondmembers, the first member is connected to a second member arranged in asame row and/or a same column as that of the first member. For example,it will be understood that in the case where a plurality of pixelcircuits and a plurality of light-emitting diodes are respectivelyarranged in a row direction and a column direction over a substrate,when a light-emitting diode is connected to a corresponding pixelcircuit, the light-emitting diode is connected to a pixel circuitarranged in a same row and a same column as that of the light-emittingdiode among the plurality of pixel circuits.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

In the accompanying drawings, for example, transformations of anillustrated shape may be expected depending on manufacturingtechnologies and/or tolerance. Therefore, embodiments should not beconstrued as being limited to a specific shape of a region illustratedin the present specification. For example, embodiments include changesin a shape caused during a manufacturing process.

FIG. 1 is a plan view of a display device 1 according to an exemplaryembodiment.

Referring to FIG. 1 , the display device 1 may include a substrate 100including a display area DA. Scan lines SL, data lines DL, and pixels PXconnected to the scan lines SL and the data lines DL may be arranged inthe display area DA of the substrate 100. The scan lines SL may extendin a row direction, transfer a scan signal to corresponding pixels PX,and may be spaced apart from each other in a column direction. The datalines DL may extend in the column direction, transfer a data signal tocorresponding pixels PX, and may be spaced apart from each other in therow direction. An extension direction of the scan lines SL may bedifferent from an extension direction of the data lines DL, and theinvention is not limited thereto. In another exemplary embodiment, thescan lines SL and the data lines DL may extend in a same direction. Thescan lines SL and the data lines DL may respectively extend indirections perpendicular to each other.

Each of the pixels PX may be connected to a corresponding scan line SLand a corresponding data line DL. In exemplary embodiments, the pixelsPX may be arranged in various patterns such as matrix configurations,zigzag configurations, etc. In an exemplary embodiment, each pixel PXmay emit light of one color, for example, may emit one of red light,blue light, green light, and white light. However, the invention is notlimited thereto and may emit light of color other than red, blue, green,and white.

The substrate 100 may include a non-display area NA around the displayarea DA. A first driver 200 and a second driver 300 may be arranged inthe non-display area NA. The first driver 200 may generate a data signaland supply a data signal to the data lines DL arranged in the displayarea DA. The second driver 300 may generate a scan signal and supply ascan signal to the scan lines SL arranged in the display area DA. Thefirst driver 200 and the second driver 300 are driving circuits and maybe manufactured as an integrated circuit chip and disposed (e.g.,mounted) on the substrate 100, or may be disposed on the non-displayarea NA of the substrate 100 while the pixels PX are provided in thedisplay area DA of the substrate 100.

FIG. 2 is a plan view of a portion of a display area DA according to anexemplary embodiment.

Referring to FIG. 2 , pixels PX (refer to FIG. 1 ) including a firstpixel PX1, a second pixel PX2, and a third pixel PX3 respectivelyemitting light of different colors may be arranged in a row directionand a column direction. The first pixel PX1, the second pixel PX2, andthe third pixel PX3 may respectively emit red light, green light, andblue light. However, the invention is not limited thereto, and anycombination of colors may be possible as long as the combinationproduces white light.

First power wirings 25 extending in the column direction over thesubstrate 100 and second power wirings 26 extending in the row directionover the substrate 100 may be arranged in the display area DA. Each ofthe first power wirings 25 is connected to pixels PX arranged in a samecolumn, and each of the second power wirings 26 is connected to pixelsPX arranged in a same row.

Each of the pixels PX1, PX2, and PX3 may include a first electrode 21, asecond electrode 22, and light-emitting diodes (“LEDs”) 40 electricallyconnected between the first electrode 21 and the second electrode 22.The LED 40 may be an LED having a size of a nano unit and may bereferred to as an ultraminiature LED. In exemplary embodiments, the LEDmay have various shapes such as a cylinder and a rectangularparallelepiped. The LED 40 is described below in more detail withreference to FIGS. 3A to 3D.

The first electrode 21 is electrically connected to a correspondingfirst power wiring 25. According to an exemplary embodiment, the firstelectrode 21 may be provided as one body with the corresponding firstpower wiring 25. The second electrode 22 is electrically connected to acorresponding second power wiring 26. According to an exemplaryembodiment, the second power wiring 26 may be arranged below the secondelectrode 22, and the second electrode 22 may be connected to thecorresponding second power wiring 26 through a contact plug.

To align the LEDs 40 between the first electrode 21 and the secondelectrode 22, a voltage may be applied to the first power wirings 25 andthe second power wirings 26. After the LEDs 40 are aligned between thefirst electrode 21 and the second electrode 22, the second power wirings26 may be divided into a plurality of pieces by openings 26 acorresponding to the pixels PX such that light emission of the LEDs 40of each pixel PX is controlled independently. Pieces of the second powerwiring 26 divided by the openings 26 a may be referred to as powerelectrodes. Each of the second power wirings 26 includes the powerelectrodes, the power electrodes being spaced apart from each other inthe row direction and being respectively connected to the secondelectrodes 22 of the pixels PX arranged in a same row.

The first electrode 21 and the second electrode 22 extend in a firstdirection (e.g., vertical direction in FIG. 2 ). Although the firstdirection in FIG. 2 is the same as an extension direction of the firstpower wiring 25, that is, the column direction, the invention is notlimited thereto and the first direction may be same as the rowdirection.

A first partition wall 31 extending in the first direction may bearranged on the first electrode 21, and a second partition wall 32extending in the first direction may be arranged on the second electrode22.

A pixel-defining layer 30 defining an emission region 70 of a pixel PXmay be arranged around the first electrode 21 and the second electrode22. An opening exposing the emission region 70 of the pixel PX may bedefined in pixel-defining layer 30 and the pixel-defining layer 30 maycover the rest of the region excluding the emission region 70. Thepixel-defining layer 30 may cover the first power wiring 25 and thesecond power wiring 26. The LEDs 40 and the first and second partitionwalls 31 and 32 may be arranged in the emission region 70. At least aportion of the first and second electrodes 21 and 22 may be arranged inthe emission region 70.

Each of the pixels PX1, PX2, and PX3 may further include a firstconnection electrode 61 on the first electrode 21 and the firstpartition wall 31, and a second connection electrode 62 on the secondelectrode 22 and the second partition wall 32. The first connectionelectrode 61 may electrically connect the first electrode 21 to a firstend of each of the LEDs 40, and the second connection electrode 62 mayelectrically connect the second electrode 22 to a second end of each ofthe LEDs 40.

FIGS. 3A to 3D are views of the LED 40 according to various embodiments.

Referring to FIG. 3A, the LED 40 according to an exemplary embodimentmay include a first electrode layer 410, a second electrode layer 420, afirst semiconductor layer 430, a second semiconductor layer 440, and anactive layer 450 between the first semiconductor layer 430 and thesecond semiconductor layer 440. As an example, the first electrode layer410, the first semiconductor layer 430, the active layer 450, the secondsemiconductor layer 440, and the second electrode layer 420 may besequentially stacked in a lengthwise direction (e.g., vertical directionin FIG. 3A) of the LED 40. In an exemplary embodiment, the length L ofthe LED 40 may be about 1 micrometer (μm) to about 10 μm, and a diameterof the LED 40 may be about 0.5 μm to about 500 μm, but the invention isnot limited thereto.

In an exemplary embodiment, the first electrode layer 410 and the secondelectrode layer 420 may be ohmic contact electrodes. However, the firstelectrode layer 410 and the second electrode layer 420 are not limitedthereto and may be Schottky contact electrodes in another exemplaryembodiment. In an exemplary embodiment, the first electrode layer 410and the second electrode layer 420 may include one or more metals suchas aluminum, titanium, indium, gold, and silver, for example. Materialsincluded in the first electrode layer 410 and the second electrode layer420 may be the same with or different from each other.

In an exemplary embodiment, the first semiconductor layer 430 mayinclude, for example, an n-type semiconductor layer, and the secondsemiconductor layer 440 may include, for example, a p-type semiconductorlayer. In an exemplary embodiment, the semiconductor layer may include asemiconductor material such as GaN, AN, AlGaN, InGaN, InN, InAlGaN, andAlInN. In an exemplary embodiment, the first semiconductor layer 430 maybe doped with n-type dopants such as Si, Ge, and Sn. In an exemplaryembodiment, the second semiconductor layer 440 may be doped with p-typedopants such as Mg, Zn, Ca, Sr, and Ba. However, the invention is notlimited thereto, and the first semiconductor layer 430 may include ap-type semiconductor layer and the second semiconductor layer 440 mayinclude an n-type semiconductor layer.

The active layer 450 may be arranged between the first semiconductorlayer 430 and the second semiconductor layer 440, and may include, forexample, a single or multiple quantum-well structure. The active layer450 is a region in which an electron and a hole recombine. As anelectron and a hole recombine, the active layer 450 may transit to alower energy level and generate light having a wavelength correspondingthereto. The active layer 450 may be located variously depending on akind of the LED 40. The invention is not limited to the above exemplaryembodiments. In an exemplary embodiment, the LED 40 may further includea separate fluorescent body layer, an active layer, a semiconductorlayer, and/or an electrode layer above and below the first semiconductorlayer 430 and the second semiconductor layer 440, for example. Lightgenerated from the active layer 450 may be emitted to an externalsurface and/or both lateral surfaces of the LED 40.

The LED 40 may further include an insulating layer 470 covering an outersurface. In an exemplary embodiment, the insulating layer 470 may coverthe active layer 450 and prevent the active layer 450 from contactingthe first electrode 21 or the second electrode 22. The insulating layer470 may prevent reduction of emission efficiency by protecting an outersurface of the LED 40 including an outer surface of the active layer450.

Referring to FIG. 3B, though the LED 40 illustrated in FIG. 3B isdifferent from the LED 40 illustrated in FIG. 3A in that the insulatinglayer 470 covers an entire outer surface of the LED 40, otherconfigurations are substantially the same as those of FIG. 3A. In theLED 40 illustrated in FIG. 3A, the insulating layer 470 covers a portionof the outer surface of the LED 40. According to an exemplaryembodiment, at least one of the first electrode layer 410 and the secondelectrode layer 420 of the LED 40 may be omitted.

Referring to FIG. 3C, the LED 40 in which one of the first electrodelayer 410 and the second electrode layer 420 has been omitted in the LED40 of FIG. 3A is illustrated. The LED 40 illustrated in FIG. 3C includesonly the first electrode layer 410 which is one of the first electrodelayer 410 and the second electrode layer 420.

In the LED 40 of FIG. 3C, the insulating layer 470 covers a portion ofan outer surface of the first electrode layer 410, and covers a portionof an outer surface of the second semiconductor layer 440. According toanother exemplary embodiment, the insulating layer 470 may cover anentire outer surface of the second semiconductor layer 440.

Referring to FIG. 3D, the LED 40 in which both the first electrode layer410 and the second electrode layer 420 in the LED 40 of FIG. 3A areomitted is illustrated. As illustrated in FIG. 3D, although theinsulating layer 470 covers entire outer surfaces of the firstsemiconductor layer 430, the active layer 450, and the secondsemiconductor layer 440, the exemplary embodiment is not limitedthereto. The insulating layer 470 may cover at least a portion of outersurfaces of the first semiconductor layer 430 and the secondsemiconductor layer 440 and expose a portion of the outer surfaces.

In the case where the first and second electrode layer 410 and 420 orthe first and second semiconductor layers 430 and 440 are exposed by theinsulating layer 470, an area through which the first and secondelectrodes 21 and 22 contact the first and second connection electrodes61 and 62 may increase.

Opposite ends of each of the LEDs 40 may respectively contact uppersurfaces of the first and second electrodes 21 and 22. The LEDs 40 maybe spaced apart from each other between the first electrode 21 and thesecond electrode 22.

In an exemplary embodiment, the first electrode layer 410 or the firstsemiconductor layer 430 arranged at the first end of the LED 40 maycontact an upper surface of the first electrode 21, and the secondelectrode layer 420 or the second semiconductor layer 440 arranged atthe second end of the LED 40 may contact an upper surface of the secondelectrode 22, for example.

Hereinafter, though the LED 40 of FIG. 3B in which the insulating layer470 covers an entire outer surface is mainly described for easyunderstanding of the invention, the description is equally applicable tothe LEDs 40 illustrated in FIGS. 3A, 3C, and 3D.

FIG. 4A is a partial cross-sectional view of the display area takenalong line A-A′ of FIG. 2 according to an exemplary embodiment.

Referring to FIGS. 2 to 4A, the first electrode 21 and the secondelectrode 22 may be arranged in parallel with each other in a firstdirection (e.g., horizontal direction FIG. 4A) over the substrate 100.Both the first electrode 21 and the second electrode 22 may extend inthe first direction. The first electrode 21 may be spaced apart from thesecond electrode 22 by a first interval g. The substrate 100 may be aninsulating substrate.

The LED 40 may be arranged on the first electrode 21 and the secondelectrode 22. The LED 40 may be electrically connected between the firstelectrode 21 and the second electrode 22. The length L of the LED 40 maybe greater than the first interval g between the first electrode 21 andthe second electrode 22 such that the first end of the LED 40 isarranged on the first electrode 21 and the second end of the LED 40 isarranged on the second electrode 22. Nevertheless, the first end of theLED 40 may be arranged on the first electrode 21, the second end may beadjacent to the second electrode 22 on the substrate 100, or the firstend of the LED 40 may be adjacent to the first electrode 21 on thesubstrate 100 and the second end may be arranged on the second electrode22, or both the first end and the second end of the LED 40 may berespectively adjacent to the first electrode 21 and the second electrode22 on the substrate 100. In this case, the first end of the LED 40 maybe electrically connected to the first electrode 21 through the firstconnection electrode 61, and the second end of the LED 40 may beelectrically connected to the second electrode 22 through the secondconnection electrode 62.

The first power wiring 25 may be arranged on the substrate 100. Thefirst power wiring 25 may be covered by the pixel-defining layer 30defining the emission region 70.

The first partition wall 31 and the second partition wall 32 may berespectively arranged on the first electrode 21 and the second electrode22. The first partition wall 31 and the second partition wall 32 may bespaced apart from each other by a second interval d. The second intervald may be equal to or greater than the length L of the LED 40 such thatthe LED 40 is arranged between the first partition wall 31 and thesecond partition wall 32. A central line between the first partitionwall 31 and the second partition wall 32 may be substantially the sameas a central line between the first electrode 21 and the secondelectrode 22.

The first partition wall 31 and the second partition wall 32 may berespectively arranged along central lines of the first electrode 21 andthe second electrode 22. The central lines are lines extending fromcenters of widths of the first electrode 21 and the second electrode 22in the first direction. In an exemplary embodiment, the first partitionwall 31 may be separated by a first distance w1 from a first edge of anupper surface of the first electrode 21, may have a thickness of asecond distance w2, and may be separated by a third distance w3 from asecond edge opposite to the first edge of the upper surface of the firstelectrode 21, for example. A sum of the first to third distances w1, w2,and w3 is the same as a width of the upper surface of the firstelectrode 21. In this case, the first distance w1 and the third distancew3 may be substantially the same with each other. The second distance w2corresponding to the thickness of the first partition wall 31 may beabout ⅓ of the width of the upper surface of the first electrode 21. Thesecond electrode 22 and the second partition wall 32 may have the samelocation relation as that of the first electrode 21 and the firstpartition wall 31.

The first and second partition walls 31 and 32 may be provided during asame process as that of the pixel-defining layer 30 by a same materialas that of the pixel-defining layer 30. Upper surfaces of the firstpartition wall 31 and the second partition wall 32 may be arranged on asubstantially same plane as an upper surface of the pixel-defining layer30. A height h of the first partition wall 31 and the second partitionwall 32 may be equal to or greater than the length L of the LED 40.Therefore, the LED 40 may be prevented from being arranged on the firstpartition wall 31 or the second partition wall 32 while the LED 40 isaligned.

An angle θ defined by the upper surface of the first electrode 21 and alateral surface of the first partition wall 31 may be 90° or less.Likewise, an angle θ defined by the upper surface of the secondelectrode 22 and a lateral surface of the second partition wall 32 maybe 90° or less. Therefore, a width, that is, a thickness of across-section of the first and second partition walls 31 and 32 may notbe reduced in a direction away from the substrate 100. FIG. 4Aillustrates that a width, that is, a thickness of a cross-section of thefirst and second partition walls 31 and 32, is constant, and an angle θdefined by the upper surface of the first and second electrodes 21 and22 and a lateral surface of the first and second partition walls 31 and32 is 90°, but the invention is not limited thereto. In an exemplaryembodiment, a width, that is, a thickness of a cross-section of thefirst and second partition walls 31 and 32, may increase in thedirection away from the substrate 100, an angle θ defined by the uppersurface of the first and second electrodes 21 and 22, and a lateralsurface of the first and second partition walls 31 and 32 may be lessthan 90°, and thereby a cross-section of the first and second partitionwalls 31 and 32 may have an inverse-tapered shape, for example. In anexemplary embodiment, an angle θ defined by the upper surface of thefirst and second electrodes 21 and 22, and a lateral surface of thefirst and second partition walls 31 and 32 may be about 70°, forexample.

Due to the first partition wall 31 on the first electrode 21 and thesecond partition wall 32 on the second electrode 22, the LED 40 may beprevented from leaning to the first electrode 21 or the second electrode22 and thereby prevented from being connected to only one of the firstelectrode 21 and the second electrode 22 while the LED 40 is aligned.The first and second partition walls 31 and 32 restrict a location ofthe LED 40 such that the first end of the LED 40 is arranged on thefirst electrode 21 and the second end of the LED 40 is arranged on thesecond electrode 22 while the LED 40 is aligned.

The first and second partition walls 31 and 32 may include an insulatingmaterial insulated from the first and second electrodes 21 and 22.Therefore, even when a voltage for alignment is applied between thefirst and second electrodes 21 and 22 while the LED 40 is aligned, anelectric field is not concentrated on the first and second partitionwalls 31 and 32. Therefore, the LED 40 is not given force directed tothe first and second partition walls 31 and 32 while the LED 40 isaligned. The first and second partition walls 31 and 32 may include aphotosensitive organic material.

The first connection electrode 61 is arranged to cover the firstelectrode 21, the first partition wall 31, and the first end of the LED40 arranged on the first electrode 21. The second connection electrode62 is arranged to cover the second electrode 22, the second partitionwall 32, and the second end of the LED 40 arranged on the secondelectrode 22. In an exemplary embodiment, the first connection electrode61 and the second connection electrode 62 may include a transparentconductive oxide, for example.

The first electrode layer 410 or the first semiconductor layer 430 ofthe LED 40 may contact the upper surface of the first electrode 21, andthe second electrode layer 420 or the second semiconductor layer 440 maycontact the upper surface of the second electrode 22. The firstelectrode layer 410 or the first semiconductor layer 430 of the LED 40may be electrically connected to the first electrode 21 through thefirst connection electrode 61, and the second electrode layer 420 or thesecond semiconductor layer 440 may be electrically connected to thesecond electrode 22 through the second connection electrode 62. Thefirst connection electrode 61 may cover the exposed first electrodelayer 410 or first semiconductor layer 430 of the LED 40, and the uppersurface of the first electrode 21. The second connection electrode 62may cover the exposed second electrode layer 420 or second semiconductorlayer 440 of the LED 40, and the upper surface of the second electrode22.

Though it is shown that the first and second connection electrodes 61and 62 cover all of the lateral surfaces and upper surfaces of the firstand second partition walls 31 and 32, this is exemplary and theinvention is not limited thereto. According to another exemplaryembodiment, depending on a manufacturing process and materials of thefirst and second connection electrodes 61 and 62, the first and secondconnection electrodes 61 and 62 may not cover the entire lateralsurfaces of the first and second partition walls 31 and 32 and mayexpose at least a portion of the lateral surfaces of the first andsecond partition walls 31 and 32. According to another exemplaryembodiment, the first and second connection electrodes 61 and 62 may notcover the upper surfaces of the first and second partition walls 31 and32 by removing a portion of a connection electrode material layerarranged on the upper surfaces of the first and second partition walls31 and 32 during a process of etching the connection electrode materiallayer for forming the first and second connection electrodes 61 and 62.Also, a height h of the first and second partition walls 31 and 32 maybe reduced by performing additional etching, e.g., dry etching on theexposed upper surfaces of the first and second partition walls 31 and32.

FIG. 4B is a partial cross-sectional view of the display area takenalong line A-A′ of FIG. 2 according to another exemplary embodiment.

Referring to FIGS. 2 to 4B, each of the pixels PX1, PX2, and PX3 mayfurther include a pixel circuit electrically connected to the LED 40 andcontrolling light emission of the LED 40 as illustrated in FIG. 4B. Anexemplary embodiment illustrated in FIG. 4B further includes the pixelcircuit in the exemplary embodiment illustrated in FIG. 3B and otherconfigurations of FIG. 4B is substantially the same as those of FIG. 3B.

The pixel circuit may include at least one thin film transistor (“TFT”)and at least one capacitor. The exemplary embodiment illustrated in FIG.4B illustrates a first TFT 120 and a second TFT 140, and capacitorelectrodes 161 and 163 on a buffer layer 101. The invention is notlimited thereto, and the pixel circuit may include three or more TFTsand/or two or more capacitors and have various structures such asadditional wirings. The first TFT 120, the second TFT 140, and thecapacitor electrodes 161 and 163 may be arranged below the LED 40.

The first TFT 120 may include a first active layer 121, a first gateelectrode 122, a first drain electrode 123, and a first source electrode124. A first gate insulating layer 102 may be arranged between the firstgate electrode 122 and the first active layer 121 for insulationtherebetween. The first gate electrode 122 on the first gate insulatinglayer 102 may overlap a portion of the first active layer 121. A secondgate insulating layer 103 and an inter-insulating layer 104 may bearranged between the first gate electrode 122, the first drain electrode123, and the first source electrode 124. The first TFT 120 may be adriving TFT driving the LED 40. The drain electrode 123 may be connectedto the second electrode 22.

The second TFT 140 may include a second active layer 141, a second gateelectrode 142, a second drain electrode 143, and a second sourceelectrode 144. The first gate insulating layer 102 is arranged betweenthe second gate electrode 142 and the second active layer 141 and mayinsulate the second gate electrode 142 from the second active layer 141.The second gate electrode 142 on the first gate insulating layer 102 mayoverlap a portion of the second active layer 141. The second gateinsulating layer 103 and the inter-insulating layer 104 may be arrangedbetween the second gate electrode 142, the second drain electrode 143,and the second source electrode 144. The second TFT 140 may be aswitching TFT.

The capacitor upper electrode 163 may be arranged in a layer in whichthe first gate electrode 122 of the first TFT 120 and the second gateelectrode 142 of the second TFT 140 are arranged. The capacitor upperelectrode 163 may be electrically connected to one of the first drainelectrode 123, the first source electrode 124, the second drainelectrode 143, and the second source electrode 144 by a connectionwiring 165. In an exemplary embodiment, the capacitor upper electrode163 may be electrically connected to the first source electrode 124 bythe connection wiring 165, for example.

The capacitor lower electrode 161 may be arranged in a layer in whichthe first active layer 121 of the first TFT 120 and the second activelayer 141 of the second TFT 140 are arranged. The capacitor lowerelectrode 161 and the capacitor upper electrode 163 may configure acapacitor. The first electrode 21 may be connected to the first powerwiring 25 and supplied with power through the first power wiring 25 asillustrated in FIG. 2 .

FIG. 5 is a partial cross-sectional view of a display device in whichfirst and second partition walls are absent according to a comparativeexample.

Referring to the comparative example of FIG. 5 , since the first andsecond partition walls do not restrict a location of the LED 40 evenwhen a separation distance g between a first electrode 21′ and a secondelectrode 22′ is less than the length L of the LED 40, the LED 40 maycontact only one of the first electrode 21′ and the second electrode 22′due to dielectrophoretic (“DEP”) force, and thereby a loose contact mayoccur. In the comparative example of FIG. 5 , a first end of the LED 40may contact a first connection electrodes 61′ and a second end of theLED 40 opposite to the first end may not be disposed on a secondconnection electrode 62′, for example.

In contrast, according to an exemplary embodiment, since the firstpartition wall 31 and the second partition wall 32 are arranged on thefirst electrode 21 and the second electrode 22, a location of the LED 40is restricted such that the first end and the second end of the LED 40are respectively arranged on the first electrode 21 and the secondelectrode 22. Therefore, an alignment degree of the LED 40 may improve.The alignment degree may be defined as a ratio of the number of LEDselectrically normally connected between the first electrode 21 and thesecond electrode 22 to the number of all LEDs arranged over thesubstrate.

FIG. 6 is a plan view of a portion of a display area DA (refer to FIG. 1) according to another exemplary embodiment.

Referring to FIG. 6 , one pixel PX (refer to FIG. 1 ) inside the displayarea DA is illustrated. The pixel PX may be the first pixel PX1 emittingred light, the second pixel PX2 emitting green light, or the third pixelPX3 emitting blue light. However, the invention is not limited theretoand the pixel PX may emit light of a different color.

The pixel PX may include the plurality of first electrodes 21, theplurality of second electrodes 22, and the plurality of LEDs 40 eachbeing electrically connected between the first electrode 21 and thesecond electrode 22 adjacent to each other. The LED 40 may be an LEDhaving a size of a nano unit and may be referred to as an ultraminiatureLED. The LED 40 may have various shapes such as a cylinder and arectangular parallelepiped.

The pixel PX includes the first power wiring 25 and the second powerwiring 26 in which an intermediate portion thereof is cut by the opening26 a. The first power wirings 25 extend in a column direction over thesubstrate, and each of the first power wirings 25 is connected to pixelsPX arranged in a same column. The second power wirings 26 extend in arow direction over the substrate, and each of the second power wirings26 is connected to pixels PX arranged in a same row.

The first electrodes 21 are electrically connected to the first powerwiring 25. According to an exemplary embodiment, the first electrodes 21may be one body with the first power wiring 25. The second electrodes 22are electrically connected to the second power wiring 26 through aconnection electrode 23. According to an exemplary embodiment, thesecond power wiring 26 may be arranged below the connection electrode23. The connection electrode 23 may be connected to a correspondingsecond power wiring 26 through a contact plug. According to anotherexemplary embodiment, depending on an arrangement of the firstelectrodes 21 and the second electrodes 22, the first electrodes 21 maynot be directly connected to the first power wiring 25 and may beconnected to the first power wiring 25 through a connection electrode.

The first electrodes 21 and the second electrodes 22 extend in a firstdirection. Though the first direction is the same as an extensiondirection of the second power wiring 26, that is, a row direction inFIG. 6 , the invention is not limited thereto and the first directionmay be same as a column direction. The first electrodes 21 and thesecond electrodes 22 may be alternately arranged in a directionperpendicular to the first direction, and a separation distance betweenthe first electrode 21 and the second electrode 22 adjacent to eachother may be constant.

To align the LEDs 40 between the first electrode 21 and the secondelectrode 22, a voltage may be applied to the first power wirings 25 andthe second power wirings 26. After the LEDs 40 are aligned between thefirst electrode 21 and the second electrode 22, the second power wirings26 may be divided into a plurality of pieces by the openings 26 acorresponding to the pixels PX such that light emission of the LEDs 40of each pixel PX is controlled independently. Pieces of the second powerwiring 26 divided by the openings 26 a may be referred to as powerelectrodes. The second power wiring 26 includes the power electrodes,the power electrodes being spaced apart from each other in the rowdirection and being connected to the connection electrode 23 of thepixels PX.

The first partition walls 31 extending in the first direction may bearranged on the first electrodes 21, and the second partition walls 32extending in the first direction may be arranged on the secondelectrodes 22.

The pixel-defining layer 30 defining the emission region 70 of a pixelPX may be arranged around the first electrodes 21 and the secondelectrodes 22. The pixel-defining layer 30 may include an openingexposing the emission region 70 of the pixel PX and cover the rest ofthe region excluding the emission region 70. The pixel-defining layer 30may cover the first power wiring 25, the second power wiring 26, and theconnection electrode 23. The LEDs 40, at least a portion of the firstand second electrodes 21 and 22, and the first and second partitionwalls 31 and 32 may be arranged in the emission region 70.

The pixel PX may further include the first connection electrodes 61 onthe first electrodes 21 and the first partition walls 31, and the secondconnection electrodes 62 on the second electrodes 22 and the secondpartition walls 32. Each of the first connection electrodes 61 mayelectrically connect a corresponding first electrode 21 to a first endof each of the LEDs 40, and each of the second connection electrodes 62may electrically connect a corresponding second electrode 22 to a secondend of each of the LEDs 40.

FIG. 7A is a partial cross-sectional view of the display area takenalong line B-B′ of FIG. 6 according to another exemplary embodiment.

The exemplary embodiment illustrated in FIG. 7A is substantially thesame as the exemplary embodiment illustrated in FIG. 4A except that aplurality of first and second electrodes 21 and 22, and a plurality offirst and second partition walls 31 a and 32 a are provided and thefirst and second partition walls 31 a and 32 a respectively includescattering particles 31 p and 32 p. Same elements are not repeatedlydescribed and only differences are mainly described.

Referring to FIGS. 6 and 7A, the first electrodes 21 and the secondelectrodes 22 may extend in the first direction on the substrate 100such that the first electrodes 21 and the second electrodes 22 areparallel to each other, and may be alternately arranged in a directionperpendicular to the first direction. The first electrodes 21 and thesecond electrodes 22 may be spaced apart from each other by the firstinterval g. The length L of the LED 40 may be greater than the firstinterval g between the first electrode 21 and the second electrode 22such that the first end of the LED 40 is arranged on the first electrode21 and the second end of the LED 40 is arranged on the second electrode22.

The substrate 100 may be an insulating substrate. As illustrated in FIG.4B, the pixel circuit may be arranged on the substrate 100.

The first partition walls 31 a and the second partition walls 32 a maybe respectively arranged on the first electrodes 21 and the secondelectrodes 22. The first partition wall 31 a may be spaced apart fromthe second partition wall 32 a by the second interval d. The secondinterval d may be equal to or greater than the length L of the LED 40such that the LED 40 is arranged between the first partition wall 31 aand the second partition wall 32 a. A central line between the firstpartition wall 31 a and the second partition wall 32 a may besubstantially the same as a central line between the first electrode 21and the second electrode 22. The first partition wall 31 a and thesecond partition wall 32 a may be respectively arranged along centrallines of the first electrode 21 and the second electrode 22.

A height h of the first partition wall 31 a and the second partitionwall 32 a may be equal to or greater than the length L of the LED 40.Therefore, the LED 40 may be prevented from being arranged on the firstpartition wall 31 a or the second partition wall 32 a while the LED 40is aligned. An angle θ defined by the upper surface of the firstelectrode 21 and a lateral surface of the first partition wall 31 a maybe 90° or less. Likewise, an angle θ defined by the upper surface of thesecond electrode 22 and a lateral surface of the second partition wall32 a may be 90° or less. Therefore, a width, that is, a thickness of across-section of the first and second partition walls 31 a and 32 a maynot be reduced in a direction away from the substrate 100.

Due to the first and second partition walls 31 a and 32 a on the firstand second electrodes 21 and 22, the LED 40 may be prevented fromleaning to the first electrode 21 or the second electrode 22 and therebyprevented from being connected to only one of the first electrode 21 andthe second electrode 22 while the LED 40 is aligned. The first andsecond partition walls 31 a and 32 a restrict a location of the LED 40such that the first end of the LED 40 is arranged on the first electrode21 and the second end of the LED 40 is arranged on the second electrode22 while the LED 40 is aligned.

The first and second partition walls 31 a and 32 a may be insulated fromthe first and second electrodes 21 and 22. The first partition walls 31a may include an organic insulating material 31 m in which scatteringparticles 31 p are dispersed, and the second partition walls 32 a mayinclude an organic insulating material 32 m in which scatteringparticles 32 p are dispersed. In an exemplary embodiment, the scatteringparticles 32 p may be same as the scattering particles 31 p, and theorganic insulating material 32 m may be same as the organic insulatingmaterial 31 m. However, the invention is not limited thereto, and inanother exemplary embodiment, the scattering particles 32 p may bedifferent from the scattering particles 31 p, and the organic insulatingmaterial 32 m may be different from the organic insulating material 31m.

In an exemplary embodiment, the organic insulating materials 31 m and 32m may be an organic material having light transmittance such as asilicon resin and an epoxy resin. The scattering particles 31 p and 32 pmay increase light extraction efficiency by scattering light incident tothe first and second partition walls 31 a and 32 a. The scatteringparticles 31 p and 32 p are not particularly limited as long as they aregenerally used, and may be, for example, TiO₂ or metal particles.

Even when a voltage for alignment is applied between the first andsecond electrodes 21 and 22 while the LED 40 is aligned, an electricfield is not concentrated on the first and second partition walls 31 aand 32 a having an insulating characteristic. Therefore, the LED 40 isnot given force directed to the first and second partition walls 31 aand 32 a while the LED 40 is aligned. Also, light emitted from the LED40 to a lateral direction and incident to the first and second partitionwalls 31 a and 32 a is scattered by the scattering particles 31 p and 32p, and thereby the light may be emitted in a front direction. Therefore,light extraction efficiency of the display device may improve.

The first and second partition walls 31 a and 32 a including the organicinsulating materials 31 m and 32 m in which the scattering particles aredispersed are applicable to the exemplary embodiments illustrated inFIGS. 2, 4A, and 4B.

FIG. 7B is a partial cross-sectional view of the display area takenalong line B-B′ of FIG. 6 according to another exemplary embodiment.

The exemplary embodiment illustrated in FIG. 7B is substantially thesame as the exemplary embodiment illustrated in FIG. 7A except for across-sectional shape of first and second partition walls 31 b and 32 b.Same elements are not repeatedly described and only differences aremainly described.

Referring to FIGS. 6 and 7B, the first electrodes 21 and the secondelectrodes 22 may extend in the first direction on the substrate 100such that the first electrodes 21 and the second electrodes 22 areparallel to each other. The first electrodes 21 and the secondelectrodes 22 may be spaced apart from each other by the first intervalg. The length L of the LED 40 may be greater than the first interval gbetween the first electrode 21 and the second electrode 22 such that thefirst end of the LED 40 is arranged on the first electrode 21 and thesecond end of the LED 40 is arranged on the second electrode 22.

The first partition walls 31 b and the second partition walls 32 b maybe respectively arranged on the first electrodes 21 and the secondelectrodes 22. The first partition wall 31 b may be spaced apart fromthe second partition wall 32 b by the second interval d. The secondinterval d may be equal to or greater than the length L of the LED 40such that the LED 40 is arranged between the first partition wall 31 band the second partition wall 32 b. A central line between the firstpartition wall 31 b and the second partition wall 32 b may besubstantially the same as a central line between the first electrode 21and the second electrode 22. The first partition wall 31 b and thesecond partition wall 32 b may be respectively arranged along centrallines of the first electrode 21 and the second electrode 22.

A height h of the first partition wall 31 b and the second partitionwall 32 b may be equal to or greater than the length L of the LED 40.Therefore, the LED 40 may be prevented from being arranged on the firstpartition wall 31 b or the second partition wall 32 b while the LED 40is aligned.

An angle θ defined by the upper surface of the first and secondelectrodes 21 and 22 and a lateral surface of the first and secondpartition wall 31 b and 32 b may be an acute angle. In an exemplaryembodiment, the angle θ may be, for example, about 70°. Therefore, awidth, that is, a thickness of a cross-section of the first and secondpartition walls 31 b and 32 b increases in a direction away from thesubstrate 100, and thereby the cross-section of the first and secondpartition walls 31 b and 32 b may have an inverse-tapered shape from anupper surface of the first and second electrodes 21 and 22.

Due to the first and second partition walls 31 b and 32 b on the firstand second electrodes 21 and 22, the LED 40 may be prevented fromleaning to the first electrode 21 or the second electrode 22 and therebyprevented from being connected on only one of the first electrode 21 andthe second electrode 22 while the LED 40 is aligned. The first andsecond partition walls 31 b and 32 b restrict a location of the LED 40such that the first end of the LED 40 is arranged on the first electrode21 and the second end of the LED 40 is arranged on the second electrode22 while the LED 40 is aligned. Therefore, a ratio in which the LED 40is electrically connected between the first electrodes 21 and the secondelectrodes 22 may be raised.

Though it is shown that the first and second connection electrodes 61and 62 cover all of the lateral surfaces and upper surfaces of the firstand second partition walls 31 b and 32 b in FIG. 7B, this is exemplaryand the invention is not limited thereto. According to another exemplaryembodiment, since the first and second partition walls 31 b and 32 bhave an inverse-tapered shape, depending on materials of the first andsecond connection electrodes 61 and 62, the first and second connectionelectrodes 61 and 62 may not cover the entire lateral surface of thefirst and second partition walls 31 b and 32 b and may expose at least aportion of the lateral surface of the first and second partition walls31 b and 32 b.

The first and second partition walls 31 b and 32 b having across-section of an inverse-tapered shape are applicable to theexemplary embodiments illustrated in FIGS. 2, 4A, and 4B.

FIG. 8 is a plan view of a portion of a display area DA according toanother exemplary embodiment.

Referring to FIG. 8 , one pixel PX (refer to FIG. 1 ) inside the displayarea DA is illustrated.

The exemplary embodiment illustrated in FIG. 8 is substantially the sameas the exemplary embodiment illustrated in FIG. 6 except for anarrangement of first and second connection electrodes 61 a and 62 a. Thesame elements are not repeatedly described and only differences aremainly described.

The first and second connection electrodes 61 a and 62 a may not coverupper surfaces of the first and second partition walls 31 and 32. Thefirst and second connection electrodes 61 a and 62 a may not cover atleast a portion of lateral surfaces of the first and second partitionwalls 31 and 32.

The first and second connection electrodes 61 a and 62 a may be arrangedonly on a region in which the first end and the second end of the LED 40will be arranged. In the first electrode 21 and/or the second electrode22 arranged in an outermost side among the first electrodes 21 and thesecond electrodes 22 arranged alternately, only a portion of theelectrode in which the LEDs 40 are arranged among portions divided bythe first and second partition walls 31 and 32 may be covered by thefirst and second connection electrodes 61 a and 62 a.

FIG. 9 is a partial cross-sectional view of the display area taken alongline C-C′ of FIG. 8 according to another exemplary embodiment.

The exemplary embodiment illustrated in FIG. 9 is substantially the sameas the exemplary embodiment illustrated in FIG. 7B except for the firstand second connection electrodes 61 a and 62 a and a capping layer 81.Same elements are not repeatedly described and only differences aremainly described.

Referring to FIGS. 8 and 9 , the first and second connection electrodes61 a and 62 a may not cover upper surfaces and at least a portion oflateral surfaces of the first and second partition walls 31 b and 32 b.

In an exemplary embodiment, an angle θ defined by the upper surface ofthe first and second electrodes 21 and 22 and a lateral surface of thefirst and second partition wall 31 b and 32 b may be an acute angle, forexample, about 70°. Therefore, a width, that is, a thickness of across-section of the first and second partition walls 31 b and 32 bincreases in a direction away from the substrate 100, and thecross-section of the first and second partition walls 31 b and 32 b mayhave an inverse-tapered shape from an upper surface of the first andsecond electrodes 21 and 22.

The pixel-defining layer 30 may be arranged on the substrate 100 and maydefine an opening exposing the emission region 70 in which the LEDs 40,and the first and second partition walls 31 b and 32 b are arranged. Theopening of the pixel-defining layer 30 may be filled with the cappinglayer 81. The capping layer 81 may cover at least an exposed portion oflateral surfaces of the first and second partition walls 31 b and 32 bnot covered by the first and second connection electrodes 61 a and 62 a.

The first and second partition walls 31 b and 32 b may include a samematerial as that of the pixel-defining layer 30. A refractive index of amaterial of the first and second partition walls 31 b and 32 b may begreater than a refractive index of a material of the capping layer 81.Therefore, light incident to, at an incident angle greater than athreshold angle, a boundary surface between the first and secondpartition walls 31 b and 32 b and the capping layer 81 is totallyreflected. Since the first and second partition walls 31 b and 32 b havea cross-section of an inverse-tapered shape, light totally reflected atthe boundary surface between the first and second partition walls 31 band 32 b and the capping layer 81 may be emitted in a front direction,that is, toward an opposite direction of the substrate.

Light emitted from the LED 40 to the lateral direction may be incidentto the first and second partition walls 31 b and 32 b, and the lightincident to the first and second partition walls 31 b and 32 b may betotally reflected at the boundary surface between the first and secondpartition walls 31 b and 32 b and the capping layer 81 and emitted inthe front direction. Therefore, the display device according to theexemplary embodiment illustrated in FIG. 9 may have improved lightextraction efficiency.

In the case where the refractive index of the material of the first andsecond partition walls 31 b and 32 b is less than the refractive indexof the material of the capping layer 81, or the first and secondpartition walls 31 b and 32 b do not have a cross-section of aninverse-tapered shape, light emitted from the LED 40 to the lateraldirection may be mixed with light emitted from an adjacent pixel PXthrough the pixel-defining layer 30 and may reduce a display imagequality of the display device.

FIGS. 10A to 101 are cross-sectional views of a process of manufacturinga display device illustrated in FIGS. 2 and 4B according to an exemplaryembodiment.

Referring to FIG. 10A, a pixel circuit including at least one TFT and atleast one capacitor may be provided over the substrate 100.

In an exemplary embodiment, the substrate 100 may include variousmaterials such as glass, metal, or plastic. According to an exemplaryembodiment, the substrate 100 may include a substrate including aflexible material. Here, the substrate of the flexible material denotesa readily wrapped and bent and foldable or rollable substrate. In anexemplary embodiment, the substrate of the flexible material may includeultrathin glass, metal, or plastic, for example.

The buffer layer 101 may be disposed on the substrate 100. In anexemplary embodiment, the buffer layer 101 may prevent impurity elementsfrom passing through the substrate 100 and penetrating to the pixelcircuit, planarize a surface of the substrate 100, and include a singlelayer or a multi-layer including an inorganic insulating material suchas SiNx and/or SiOx. In another exemplary embodiment, the buffer layer101 may be omitted.

The first TFT 120 and the second TFT 140 may be disposed on the bufferlayer 101. The first TFT 120 may include the first active layer 121, thefirst gate electrode 122, the first drain electrode 123, and the firstsource electrode 124. The second TFT 140 may include the second activelayer 141, the second gate electrode 142, the second drain electrode143, and the second source electrode 144.

The first active layer 121 and the second active layer 141 may bedisposed on the buffer layer 101 by a semiconductor material. Thesemiconductor material may be an inorganic semiconductor material suchas amorphous silicon or polycrystalline silicon, an organicsemiconductor material, or an oxide semiconductor material. The firstactive layer 121 and the second active layer 141 may include a drainregion and a source region doped with B or P ions, for example, and achannel region therebetween.

The first gate insulating layer 102 may be arranged on the buffer layer101 to cover the first active layer 121 and the second active layer 141.

In an exemplary embodiment, the first gate electrode 122 and the secondgate electrode 142 may include a single layer or a multi-layer includingone or more materials among Al, Pt, Pd, Ag, Mg, Au, Ni, Nd, Jr, Cr, Li,Ca, Mo, Ti, W, and Cu, for example.

The second gate insulating layer 103 may be arranged on the first gateinsulating layer 102 to cover the first gate electrode 122 and thesecond gate electrode 142.

The first gate insulating layer 102 and the second gate insulating layer103 may include a single layer or a multi-layer including an inorganicinsulating material. In an exemplary embodiment, the first gateinsulating layer 102 may include SiO₂, SiNx, SiON, Al₂O₃, TiO₂, Ta₂O₅,HfO₂, and/or ZrO₂, for example.

The inter-insulating layer 104 may include a single layer or amulti-layer including an organic insulating material on the second gateinsulating layer 103. The inter-insulating layer 104 may include asingle layer or a multi-layer including an inorganic insulatingmaterial. In another exemplary embodiment, one of the second gateinsulating layer 103 and the inter-insulating layer 104 may be omitted.

The first drain electrode 123 and the first source electrode 124, andthe second drain electrode 143 and the second source electrode 144 maybe disposed on the inter-insulating layer 104. The first drain electrode123 and the first source electrode 124 may be respectively connected tothe drain region and the source region of the active layer 121 throughcontact plugs passing through the first gate insulating layer 102, thesecond gate insulating layer 103, and the inter-insulating layer 104.The second drain electrode 143 and the second source electrode 144 maybe respectively connected to the drain region and the source region ofthe active layer 141 through contact plugs passing through the firstgate insulating layer 102, the second gate insulating layer 103, and theinter-insulating layer 104.

The first drain electrode 123 and the first source electrode 124, andthe second drain electrode 143 and the second source electrode 144 mayinclude a same material as that of the first and second gate electrodes122 and 142. In an exemplary embodiment, the first drain electrode 123and the first source electrode 124, and the second drain electrode 143and the second source electrode 144 may include metal, an alloy, a metalnitride, a conductive metal oxide, a transparent conductive material,etc.

The capacitor lower electrode 161 may be disposed on the buffer layer101. The capacitor lower electrode 161 may be provided simultaneouslywith the first active layer 121 and the second active layer 141 by asame material as that of the first active layer 121 and the secondactive layer 141. However, the invention is not limited thereto and thecapacitor lower electrode 161 may be provided during a process differentfrom a process of the first active layer 121 and the second active layer141 by a material different from the material of the first active layer121 and the second active layer 141.

The first gate insulating layer 102 may cover the capacitor lowerelectrode 161, and the capacitor upper electrode 163 overlapping thecapacitor lower electrode 161 may be disposed on the first gateinsulating layer 102. The capacitor upper electrode 163 may be providedsimultaneously with the first and second gate electrodes 122 and 142 bya same material as that of the first and second gate electrodes 122 and142. However, the invention is not limited thereto and the capacitorupper electrode 163 may be provided during a process different from aprocess of the first and second gate electrodes 122 and 142 by amaterial different from that of the first and second gate electrodes 122and 142.

The second gate insulating layer 103 and the inter-insulating layer 104may be arranged on the capacitor upper electrode 163, and the connectionwiring 165 may be disposed on the inter-insulating layer 104. Theconnection wiring 165 may be electrically connected to the capacitorupper electrode 163 through a contact plug passing through the secondgate insulating layer 103 and the inter-insulating layer 104. Theconnection wiring 165 may be provided simultaneously with the firstdrain electrode 123 and the first source electrode 124, and the seconddrain electrode 143 and the second source electrode 144 by a samematerial as that of the first drain electrode 123 and the first sourceelectrode 124, and the second drain electrode 143 and the second sourceelectrode 144. Though not shown, the connection wiring 165 may beelectrically connected to one of the first drain electrode 123, thefirst source electrode 124, the second drain electrode 143, and thesecond source electrode 144. In an exemplary embodiment, the capacitorupper electrode 163 may be electrically connected to the first sourceelectrode 124 through the connection wiring 165, for example.

Though not shown in FIG. 10A, according to an exemplary embodiment, thesecond power wiring 26 (refer to FIG. 2 ) may be disposed on theinter-insulating layer 104. The second power wiring 26 may be providedduring a same process as that of the connection wiring 165 by a samematerial as that of the connection wiring 165.

Referring to FIG. 10B, a passivation layer 105 covering the first andsecond TFTs 120 and 140 may be disposed on the inter-insulating layer104. The passivation layer 105 may include a single layer or amulti-layer including an organic insulating material or an inorganicinsulating material. The passivation layer 105 may be provided byalternating an organic insulating material and an inorganic insulatingmaterial.

A contact hole CH exposing a portion of the first drain electrode 123 ofthe first TFT 120 may be defined in the passivation layer 105. Thoughnot shown in FIG. 10B, a contact hole exposing a portion of the secondpower wiring 26 may be defined in the passivation layer 105.

Referring to FIG. 10C, the first electrode 21, the second electrode 22,and the first power wiring 25 may be disposed on the passivation layer105.

A first conductive layer may be disposed on the passivation layer 105.

In an exemplary embodiment, the first conductive layer may be atransparent conductive layer including at least one transparentconductive oxide among indium tin oxide (“ITO”), indium zinc oxide(“IZO”), zinc oxide (ZnO), indium oxide (In₂O₃), indium gallium oxide(“IGO”), and aluminum zinc oxide (“AZO”), for example. In an exemplaryembodiment, the first conductive layer may include at least one metalamong Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Jr, Cr, Li, Ca, Mo, Ti, W, Cu, andan alloy thereof, for example. The first conductive layer may fill thecontact hole CH defined in the passivation layer 105.

The first electrode 21, the second electrode 22, and the first powerwiring 25 may be provided by performing photolithography on the firstconductive layer.

The second electrode 22 may be electrically connected to the first drainelectrode 123 of the first TFT 120 in the lower layer. Though not shown,the second electrode 22 may be electrically connected to the secondpower wiring 26 of the lower layer through a contact plug.

Referring to FIG. 10D, the first and second partition walls 31 and 32may be respectively disposed on the first and second electrodes 21 and22, and the pixel-defining layer 30 may be provided outside the emissionregion 70 in which the first and second electrodes 21 and 22 areprovided.

An organic insulating layer may be disposed entirely on the substrate100. An opening exposing the emission region 70 and the first and secondpartition walls 31 and 32 may be defined by performing aphotolithography process on the organic insulating layer.

According to another exemplary embodiment, a photosensitive organicinsulating layer may be provided by coating a photosensitive organicinsulating layer entirely on the substrate 100 and then performing softbake on the photosensitive organic insulating layer. A photosensitiveorganic pattern may be provided by aligning a mask on the photosensitiveorganic insulating layer, then exposing the photosensitive insulatinglayer to light through the mask, and developing the same. The first andsecond partition walls 31 and 32, and the pixel-defining layer 30including the photosensitive organic insulating material may be providedby performing hard bake on the photosensitive organic pattern. The firstand second partition walls 31 and 32 may be simultaneously providedduring a same process as that of the pixel-defining layer 30 by a samematerial as that of the pixel-defining layer 30.

A slope angle of the lateral surface of the first and second partitionwalls 31 and 32 may be adjusted by adjusting exposure energy and a focalposition of an exposure beam when exposing the photosensitive organicinsulating layer to light. In an exemplary embodiment, when exposureenergy is raised, a slope angle of the lateral surface of the first andsecond partition walls 31 and 32 becomes smaller than 90°, and therebythe first and second partition walls 31 and 32 having a cross-section ofan inverse-tapered shape may be provided, for example. When a focalposition of an exposure beam is offset, a slope angle of the lateralsurface of the first and second partition walls 31 and 32 becomesgreater than 90°, and thereby the first and second partition walls 31and 32 having a cross-section of a tapered shape may be provided.

Referring to FIG. 10E, the LEDs 40 may be transferred onto the firstelectrode 21 and the second electrode 22 by putting a solvent 90including the LEDs 40 to the emission region 70.

In an exemplary embodiment, the solvent 90 may be one or more amongacetone, water, and toluene, for example, but is not limited thereto. Inan exemplary embodiment, the solvent 90 may be a material which may beevaporated by room temperature or heat, for example. In an exemplaryembodiment, the solvent 90 may be in the form of ink or paste.

FIG. 11 is a cross-sectional view for explaining a process ofself-aligning of a light-emitting diode according to an exemplaryembodiment. An electric field E may be generated between the firstelectrode 21 and the second electrode 22 by applying power V between thefirst power wiring 25 (refer to FIGS. 2, 6 and 8 ) connected to thefirst electrode 21 and the second power wiring 26 (refer to FIGS. 2, 6and 8 ) connected to the second electrode 22. The power V may be anexternal supply source or an inner power source of the display device 1.The power V may be an alternating current power source including apreset amplitude and a preset period, or a direct current power source.The direct current power source may be repeatedly applied between thefirst electrode 21 and the second electrode 22 such that the power V hasa waveform having a preset amplitude and a preset period.

When the power V is applied between the first power wiring 25 and thesecond power wiring 26, a potential difference occurs by electricpolarities of the power V respectively applied to the first power wiring25 and the second power wiring 26, and the electric field E is generatedbetween the first electrode 21 and the second electrode 22. Dipolarityis induced to the LED 40 by non-uniform electric field E, and the LED 40is given force directed to a side in which a gradient of the electricfield E is large or a side in which a gradient of the electric field Eis small by the DEP force. The electric field E is strong at an edge ofthe first electrode 21 and the second electrode 22, and accordingly,strong DEP force acts thereon. Therefore, the LED 40 is given DEP forcesuch that the first end is arranged on the first electrode 21 and thesecond end is arranged on the second electrode 22.

An insulating plane 110 illustrated in FIG. 11 may be an upper surfaceof the insulating substrate 100 illustrated in FIG. 4A or an uppersurface of the insulating layer 105 arranged on the substrate 100 asillustrated in FIG. 4B.

According to another exemplary embodiment, the second power wiring 26may be omitted. In this case, a first polarity of the power V may beapplied to the first power wiring 25, and a second polarity of the powerV may be applied to the second electrode 22 through a pixel circuit.

Referring to FIG. 10F, the solvent 90 may be evaporated by roomtemperature or heat, and the LED 40 may be self-aligned on the firstelectrode 21 and the second electrode 22 by DEP force. The first end andthe second end of the LED 40 may respectively surface-contact an uppersurface of the first electrode 21 and an upper surface of the secondelectrode 22.

Referring to FIG. 10G, a second conductive layer 60 and a photoresistlayer PR are sequentially stacked entirely over the substrate 100, andthe photoresist layer PR may be patterned by a mask (not shown). Someregion of the photoresist layer PR is removed and only a regioncorresponding to the first and second connection electrodes 61 and 62(refer to FIG. 10H) may remain. According to another exemplaryembodiment, the second conductive layer 60 may be provided inside theopening of the pixel-defining layer 30, that is, inside the emissionregion 70.

In an exemplary embodiment, the second conductive layer 60 may be atransparent conductive layer including at least one transparentconductive oxide among ITO, IZO, ZnO, In₂O₃, IGO, and AZO, for example.In an exemplary embodiment, the second conductive layer 60 may be metalincluding one of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, and acombination thereof, for example. The photoresist layer PR may be apositive or negative photosensitive organic material.

Referring to FIG. 10H, the first connection electrode 61 and the secondconnection electrode 62 may be provided by patterning the secondconductive layer 60 by the patterned photoresist layer PR as a mask.

The first and second connection electrodes 61 and 62 may cover the firstand second electrodes 21 and 22, the first and second partition walls 31and 32, and the first and second ends of the LED 40. The firstconnection electrode 61 electrically connects the first end of the LED40 to the first electrode 21, and the second connection electrode 62electrically connects the second end of the LED 40 to the secondelectrode 22.

A conductive material of the second conductive layer 60 remainingbetween the LED 40 and the passivation layer 105 may be removed byperforming wet etching during a patterning process of the secondconductive layer 60.

After the LED 40 is arranged on the first and second electrodes 21 and22 by self-alignment and electrically connected between the first andsecond electrodes 21 and 22 by the first and second connectionelectrodes 61 and 62, the opening 26 a illustrated in FIG. 2 may bedefined in the second power wiring 26 to divide the second power wiring26 for each pixel. The second power wiring 26 may be divided into powerelectrodes by the opening 26 a, the power electrodes being spaced apartfrom each other in the row direction. The power electrode is connectedto the second electrode 22 of a corresponding pixel.

According to an example, the opening 26 a may be defined by removing aportion of the second power wiring 26 with a laser. According to anotherexemplary embodiment, the opening 26 a may be defined by forming, in thepassivation layer 105, a contact hole exposing a portion of the secondpower wiring 26 corresponding to the opening 26 a, and removing theportion of the second power wiring 26 exposed by the contact hole duringthe patterning process of the second conductive layer 60.

Referring to FIG. 10I, the capping layer 81 may be provided to cover theemission region 70. The capping layer 81 may be allowed not todeteriorate light extraction efficiency by making the capping layer 81transparent or semi-transparent with respect to a visible wavelength. Inan exemplary embodiment, the capping layer 81 may include an organicinsulating material, for example, an epoxy, poly(methyl methacrylate)(“PMMA”), benzocyclobutene (“BCB”), polyimide, and polyester, but is notlimited thereto.

A refractive index of a material of the capping layer 81 may be lessthan a refractive index of a material of the first and second partitionwalls 31 b and 32 b (refer to FIG. 9 ). Light incident, at an incidentangle greater than a threshold, to a boundary surface between the firstand second partition walls 31 b and 32 b and the capping layer 81 istotally reflected. In the case where the first and second partitionwalls 31 b and 32 b have a cross-section of an inverse-tapered shape,light totally reflected at the boundary surface between the first andsecond partition walls 31 b and 32 b and the capping layer 81 may beemitted in a front direction, that is, toward an opposite direction ofthe substrate.

An optical layer 82 and a protective layer 83 may be sequentiallydisposed on the capping layer 81. The optical layer 82 blocking externallight may be disposed on the capping layer 81. According to an exemplaryembodiment, the optical layer 82 may be an RGB color filtercorresponding to light emitted from a pixel PX. The color filter may beprovided by patterning a color photoresist layer or spraying color ink.According to another exemplary embodiment, the optical layer 82 may be apolarization plate.

The protective layer 83 may be disposed on the optical layer 82. Theprotective layer 83 may include an encapsulation function and may beprovided over an entire surface of the substrate 100. The protectivelayer 83 may include an organic material or an inorganic material, ormay be provided by alternating the organic material and the inorganicmaterial.

In the exemplary embodiments, an arrangement of the first and secondelectrodes is not limited to the exemplary embodiments illustrated inFIGS. 2 and 6 , and may have various layouts depending on a size anddensity of the LEDs.

According to various embodiments, an alignment degree of anultraminiature LED may be raised by arranging partition walls which mayprevent misalignment of the ultraminiature LED on a pair of electrodes.Also, a display device which has improved light extraction efficiency bypartition walls of an inverse-tapered shape may be provided.

Although the invention has been described with reference to theexemplary embodiments illustrated in the drawings, this is merelyprovided as an example and it will be understood by those of ordinaryskill in the art that various changes in form and details andequivalents thereof may be made therein without departing from thespirit and scope of the invention as defined by the following claims.

What is claimed is:
 1. A display device comprising: a substrate; a firstelectrode on a surface of the substrate; a first structure on the firstelectrode; a second electrode on the surface of the substrate and spacedapart from the first electrode; a second structure on the secondelectrode; and a light-emitting diode on the first electrode and thesecond electrode, wherein the light-emitting diode is spaced apart fromthe first structure and the second structure, wherein a height of anupper surface of the first structure and the second structure from thesurface of the substrate is greater than a height of an upper surface ofthe light-emitting diode from the surface of the substrate, wherein thelight-emitting diode overlaps the first electrode in a directionperpendicular to the surface of the substrate, and wherein thelight-emitting diode overlaps the second electrode in the directionperpendicular to the surface of the substrate.
 2. The display device ofclaim 1, wherein an interval between the first electrode and the secondelectrode is less than a length of the light-emitting diode.
 3. Thedisplay device of claim 1, wherein an interval between the firststructure and the second structure is greater than a length of thelight-emitting diode.
 4. The display device of claim 1, wherein a widthof a cross-section of the first structure and the second structure isnot reduced in a direction that extends away from the substrate.
 5. Thedisplay device of claim 1, wherein a first width of the upper surface ofthe first structure and the second structure is greater than a secondwidth of a lower surface of the first structure and the secondstructure.
 6. The display device of claim 1, wherein each of the firststructure and the second structure comprises an organic insulatingmaterial in which scattering particles are dispersed.
 7. The displaydevice of claim 1, further comprising: a first connection electrode onthe first electrode; and a second connection electrode on the secondelectrode.
 8. The display device of claim 7, wherein the firstconnection electrode contacts the first electrode and a first end of thelight-emitting diode, and the second connection electrode contacts thesecond electrode and a second end of the light-emitting diode oppositeto the first end.
 9. The display device of claim 7, wherein at least aportion of the first connection electrode is on the first structure, andwherein at least a portion of the second connection electrode is on thesecond structure.
 10. The display device of claim 1, further comprising:a pixel-defining layer over the substrate and in which an openingexposing an emission region is defined, wherein the light-emittingdiode, the first structure, and the second structure are arranged in theemission region.
 11. The display device of claim 10, wherein the firststructure and the second structure comprise a same material as that ofthe pixel-defining layer.
 12. The display device of claim 10, furthercomprising: a capping layer filling the opening of the pixel-defininglayer and covering lateral surfaces of the first structure and thesecond structure.
 13. The display device of claim 12, wherein arefractive index of a material of the first structure and the secondstructure is greater than a refractive index of a material of thecapping layer.
 14. A display device comprising: a substrate; a firstelectrode on a surface of the substrate; a first structure on the firstelectrode; a second electrode on the surface of the substrate and spacedapart from the first electrode; a second structure on the secondelectrode; and a light-emitting diode on the first electrode and thesecond electrode, wherein the light-emitting diode is spaced apart fromthe first structure and the second structure, wherein a height of anupper surface of the first structure and the second structure from thesurface of the substrate is greater than a height of an upper surface ofthe light-emitting diode from the surface of the substrate, and whereinthe light-emitting diode overlaps a space between the first electrodeand the second electrode.
 15. The display device of claim 14, whereinthe light-emitting diode overlaps the first electrode in a directionperpendicular to the surface of the substrate, and wherein thelight-emitting diode overlaps the second electrode in the directionperpendicular to the surface of the substrate.